The embodiments herein relates to stabilizing formation laminae layers in coal seam wellbores, in particular, to stabilize formation laminae in coal seam wellbores to prevent or reduce the production of eroded material.
Non-traditional sources of hydrocarbons are playing an increasingly important role in the oil and gas industry. Such non-traditional sources include gas hydrates, heavy oil, bitumen, and coal bed methane in coal seams. Coal bed methane in particular is becoming an increasingly important energy source, with the total coal seams in the United States estimated to be between 400 and 850 trillion cubic feet, as well as many trillion cubic feet abroad.
Coal bed methane content in coal seams generally increases the deeper the seam is located in a subterranean formation, as well as with the age of the coal seam. In many instances deep coal seams are located in a formation having a striated or layered profile. For example, coal seams may be located beneath various layers of formation comprising silt, clay, sand, shale, and/or siltstone, among other formation types, as well as aquifers or water tables used for drinking water, for example. The coal seams themselves may be located between such formation layers. These formation layers may be referred to as “laminae” or “formation laminae.” Laminae containing excessive clay is particularly susceptible to freshwater contact due its insufficient salinity, allowing more water molecules to occupy the interstitial space between the laminae layers and cause swelling. As a result of such freshwater contact, the laminae may quickly undergo sloughing or other erosion, creating “eroded material,” which may be in the form of fine to coarse particulate matter that has become disassociated from the laminae or solubilized material that takes on a viscous paste-like quality in fluid.
In order to extract the methane from a coal seam, a wellbore must be drilled through the laminae and the aquifers to reach the coal seams. Stimulation operations then follow, which may involve hydraulic fracturing, acidizing, fracture acidizing, or combinations thereof. Hydraulic fracturing generally includes injecting or pumping a viscous fracturing fluid into a portion of the subterranean formation at a rate and pressure such that fractures are formed or enhanced into the portion of the subterranean formation. The fracture pressure causes the formation to crack which allows the fracturing fluid to enter and extend the crack further into the formation. The fractures tend to propagate as vertical and/or horizontal cracks located radially outward from the wellbore.
During drilling and stimulation operations, the formation laminae may be exposed to freshwater from the water table through which the wellbore was drilled, thereby forming eroded material. This eroded material may enter the wellbore and interfere with operational equipment (e.g., clogging equipment, for example). The eroded material may also collect within the wellbore, such as within the created fractures and reduce fracture conductivity, thus reducing the methane production of the coal seam wellbore. Moreover, continued exposure to freshwater may result in more and more accumulation of eroded material within the wellbore. Such accumulation may cause the need for frequent and costly, economically and in terms of operator time, workovers or other remedial action. Traditional clay and fines stabilizers have been ineffective at stabilizing the formation laminae when it becomes exposed to freshwater. This may be because stabilizing the laminae may require more than just standard ion exchange by the clay and fines stabilizer, but also physical bonding or cohesion to overcome the expansion caused by the swelling of the laminae when exposed to freshwater.